Hi, I have two puppies, dog & bitch, planning to have her spayed. However, I also have an adult, spayed bitch.
Will it make the female pup dominant over the older bitch, who is already of a (sweet) submissive nature?
Would the boy still be interested in the entire bitch if he is neutered? How long before he's sterile, approximately? Will he start mounting behavior etc?
Thanks for your thoughts.

In general bitches seem to have less problems with being neutered than do dogs, so if you have to do one or the other I would do the bitch, you are also less likely to have bitch on bitch problems if they are both neutered, as to which of the bitches will be boss is up to them and unless it seems that one will be damaged you would be best to leave them to sort it out. If you can leave the spay until after her first season, kennel the dog if you need, to give her a chance to grow up it is generally thought better.

There is a likely hood a castrated dog would be interested in the bitches and there is also a chance he would become interesting to both your bitches and other dogs by developing what is called feminisation syndrome, which makes him seem to other dogs like a bitch in season causing the dogs to mount him and the bitches to be aggressive.

If you do do the dog it is about 3 months before he is sterile and it is more than likely he will still develop the mounting behaviour, and on occasion he may not grow out of it.